Circular dependency injection angular 2

问题:

I've been struggling around injecting services into each other. The following blog Circular Dependency in constructors and Dependency Injection is kind of confusing where it says

One of the two objects is hiding another object C

I get the following error while injecting Service class into each other

Can't resolve all parameters for PayrollService: (SiteService, StorageService, SweetAlertService, ?)

//abstractmodal.service.ts
@Injectable()
 export abstract class AbstractModel {

   abstract collection = [];

   constructor(private siteService: SiteService, private storageService: StorageService,
                private sweetalertService: SweetAlertService) {}


   setCollectionEmpty() {
      this.collection = [];
    }
}
//account-payable.service.ts
@Injectable()
export class AccountPayableService extends AbstractModel {

   public collection = [];

   constructor(private sS: SiteService,private stS: StorageService, private sws: SweetAlertService,
            private accpPoService: PayablePurchaseOrderService, private attachmentService: AttachmentService,
            private injectorService: InjectorService) { 
         super(sS, stS, sws);
     }
}
//injector.service.ts
@Injectable()
export class InjectorService {
   constructor(private payrollService: PayrollService) {}

   cleanPayrollCollection() {
     this.payrollService.setCollectionEmpty();
   }
}
//payroll.service.ts
@Injectable()
export class PayrollService extends AbstractModel {

   public collection = [];

   constructor(private sS: SiteService,private stS: StorageService, private sws: SweetAlertService,
            private accpService: AccountPayableService) { 
    super(sS, stS, sws);
   }
}

Your comments and answered will be appreciated a lot.

Thanks

回答1:

You can workaround circular dependencies by injecting Injector instead of one of the services that cause the circular dependency

private payrollService:PayrollService;
constructor(/*private payrollService:PayrollService*/ injector:Injector) {
  setTimeout(() => this.payrollService = injector.get(PayrollService));
}

回答2:

In my case (Angular 4 in an Ionic project) even injecting the service just before it's usage (upon user interaction) was not working (Same "Can't resolve all parameters..." at startup).

What worked for me was to inject (and thus provide) the service by name.

So in my app module :

...
providers: [{provide: "MyServiceName", MyServiceClass}],
...

And when needed :

const myService: MyServiceClass = injector.get("MyServiceName");
...

回答3:

I know the post is old but thanks anyways above solution has worked for me as i had cyclic dependency problem so i have to use injector to avoid creating mediator service to communicate, Although one correction in above solution

From Angular 5 onwards we need to use:

providers: [{provide: "MyServiceName",useclass: MyServiceClass}],

and then

injector.get('MyServiceName')

although get is derpecated